System and method for arc detection and intervention in solar energy systems

ABSTRACT

An arc detection and intervention system for a solar energy system. One or more arc detectors are strategically located among strings of solar panels. In conjunction with local management units (LMUs), arcs can be isolated and affected panels disconnected from the solar energy system.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/075,093, filed Mar. 29, 2011, and entitled“System and Method for Arc Detection and Intervention in Solar EnergySystems,” which claims the benefit of Prov. U.S. patent application Ser.No. 61/446,440, filed Feb. 24, 2011, and entitled “System and Method forArc Detection and Intervention in Large Solar Energy Systems,” theentire disclosures of which applications are incorporated herein byreference.

COPYRIGHT NOTICE/PERMISSION

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure as it appears in the U.S. Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

FIELD OF THE TECHNOLOGY

This disclosure relates to various embodiments of solar energy systemsand more particularly to the detection of arcs within photovoltaicpanels and the isolation and disconnection of these panels from thesystems.

BACKGROUND

Solar energy systems are often plagued by arcing. In most cases, thearcing occurs inside the solar panels. This problem can affect theperformance and safety of the whole system, and it can even lead toshut-offs due to sporadic short circuits. Arcing often occurs when solarpanels have become cracked or damaged, permitting water to leak into thepanel. The presence of water may cause a short circuit of the siliconwafers to the frame or to the underlying structure, resulting in arcing.What is needed is a system and method by which an arc can be found andisolated from the rest of the system, hence improving system performanceand reducing safety risks such as the risk of fire.

SUMMARY OF THE DESCRIPTION

Embodiments of an arc detection and intervention system for a solarenergy system are disclosed. One or more arc detectors are strategicallylocated among strings of solar panels. In conjunction with systemmanagement units and local management units (LMUs), arcs can be isolatedand affected panels disconnected from the solar energy system.

These and other objects and advantages will become clear to thoseskilled in the art in view of the description of the best presentlyknown mode of carrying out the inventions and the industrialapplicability of the preferred embodiment as described herein and asillustrated in the figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The purposes and advantages of presented inventions will be apparentfrom the following detailed description in conjunction with the appendedfigures of drawings, in which:

FIG. 1 shows a representative photovoltaic system;

FIG. 2 shows the interior of a representative enhanced photovoltaicpanel;

FIG. 3 shows an overview of an photovoltaic system;

FIG. 4 shows a detailed view of a representative arc detector; and

FIG. 5 shows a testing process for detecting arcs within photovoltaicsystem.

In the various figures of the drawings, like references are used todenote like or similar elements or steps.

DETAILED DESCRIPTION

In the following description and in the accompanying drawings, specificterminology and drawing symbols are set forth to provide a thoroughunderstanding of the present invention. In some instances, theterminology and symbols can imply specific details that are not requiredto practice the invention.

FIG. 1 illustrates a representative photovoltaic system 100, accordingto one aspect of the system and method disclosed herein. Photovoltaicsystem 100 is built from a few components, including photovoltaicmodules 101 a, 101 b . . . 101 n, local management unit units 102 a, 102b . . . 102 n, an inverter 103, and system management unit 104.

In one approach, the system management unit 104 is part of the inverter103, the combiner box 106, local management units 102, or a stand-aloneunit. The solar modules 101 a, 101 b . . . 101 n are connected inparallel to the local management units 102 a, 102 b . . . 102 nrespectively, which are connected in series to form a string bus 105,which eventually is connected to an inverter 103 and the systemmanagement unit 104.

In FIG. 1, the string bus 105 can be connected to the inverter 103directly or as part of a mesh network or combiner boxes or fuse boxes(not shown). An isolated local management unit can be used as a combinerbox 106 to adjust all voltages before connecting to the inverter 106;or, a single or multi-string inverter can be used. To limit the changesin the voltage of the bus, the system management unit 104 may assign adifferent phase for each of the local management units 102 a, 102 b . .. 102 n. In one approach, at any given time, a maximum of apredetermined number of solar modules 101 (i.e., one single solar panel)are disconnected from the string bus 105.

In one approach, beyond the panel connection, the local management unitscan have the signal inputs (not shown), including but not limited toduty cycle, phase, and synchronization pulse (for example, to keep thelocal management units synchronized). In one approach, the phase and thesynchronization pulse are used to further improve performance, but thelocal management units 102 can work without them.

In one approach, the local management units may provide output signals.For example, the local management units 102 may measure current andvoltage at the module side and optionally measure current and voltage inthe string side. The local management units 102 may provide othersuitable signals, including but not limited to measurements of light,temperature (both ambient and module), etc.

In one approach, the output signals from the local management units 102are transmitted over a power line (for example, via a power linecommunication (PLC)), or transmitted wirelessly.

In one approach, the system management unit 104 receives sensor inputsfrom light sensor(s), temperature sensor(s), one or more each forambient, solar module or both, to control the photovoltaic system 100.In one approach, the signals may also include synchronization signals.For example, using the described methods, the local management unit canbe a non-expensive and reliable device that can increase the throughputof a photovoltaic solar system by a few (for example, single or lowdouble digits) percentage points. These varied controls also allowinstallers using this type of system to control the VOC (open circuitvoltage) by, for example by shutting off some or all modules. Forexample, by using the local management units 102 of the system 100, afew modules can be disconnected from a string if a string is approachesthe regulatory voltage limit, permitting more modules to be installed ina string.

In some approaches, local management units 102 can also be used withinthe solar panel to control the connection of solar cells attached tostrings of cells within the solar panel.

FIG. 2 shows the interior of a representative enhanced solar panel 200,according to one aspect of the system and method disclosed herein, withstandard solar module 101 x and local management unit (LMU) 102 x. LMU102 x can be integrated into a junction box (Jbox) or, in some cases,into the panel 200 itself. LMU 102 x provides two connectors 112 and 114for serial connections with other local management units 102 to connectto string bus 105. The controller 109 controls the states of theswitches Q1 106 and Q2 108. When the controller 109 turns on the switch106, the module voltage and the capacitor C1 110 are connected inparallel to the connectors 112 and 114. The output voltage between theconnectors 112 and 114 is substantially the same as the output panelvoltage. During the period the switch 106 is turned off (open), thecontroller 109 turns on (closes) the switch 108 to provide a path arounddiode D1 107 to improve efficiency. While the switch 106 is open, thepanel voltage charges the capacitor C1 110, such that when the switch106 is open, both the solar module 101 x and the capacitor 110 providecurrent going through the connectors 112 and 114, allowing a currentlarger than the current of the solar panel 200 to flow in the string(the string bus 105). When the switch 106 is open, the diode D1 107 alsoprovides a path between the connectors 112 and 114 to sustain current inthe string, even if the switch 108 is open for some reason.

In one approach, the controller 109 is connected (not shown in FIG. 2)to the panel voltage to obtain the power for controlling the switches Q1106 and Q2 108. In one approach, the controller 109 is further connected(not shown in FIG. 2) to at least one of the connectors to transmitand/or receive information from the string. In one approach, thecontroller 109 includes sensors (not shown in FIG. 2) to measureoperating parameters of the solar panel, such as panel voltage, panelcurrent, temperature, light intensity, etc.

FIG. 3 shows an overview of a representative system 300, according toone aspect of the system and method disclosed herein. System 300 hassystem management unit 104 and multiple strings 310 a-n, each stringcontaining multiple panels 101 with associated LMUs 102. Additionally,arc detectors such as, for example, 301, 302, 303, and 304 are insertedinto system 300. In some cases, only a single arc detector 301 isincluded in the entire system 300, and the location of a problem isdetermined by turning individual units on and off, as described later.In other cases, however, to speed up the process of arc detection, eachstring 310 a-n may have its own associated arc detector. In some cases,in system 300, multiple combiner boxes 106 may feed into a singleinverter 103, so different locations in the wiring of the system can bechosen for the location of the arc detector(s), depending on the designof the specific system.

FIG. 4 shows a more detailed view of a representative arc detector 400,according to the system and method disclosed herein. Arc detector 400 isjust one example of a suitable device for arc detectors 301, 302, 303,and 304. Typically, one of two main approaches is taken. A couplingdevice such as device 402 or device 403 may be inserted in the wiring401 of system 400. Device 402 is a Rogowski coil, a type of transformerthat may be clipped onto a wire, wherein the unbroken wire forms theprimary winding. Device 403 is a standard type of transformer thatrequires that the wire be cut and the device inserted into the circuit.Both devices 402 and 403 deliver an output signal to a circuit 405 ofarc detector box 404. Many such detector boxes 404 are currently knownin the art; see, for example, U.S. Pat. Nos. 6,683,766, 5,629,824,5,619,105, 5,280,404, and 5,121,282 that describe some of many possiblevarious types of arc detection circuits. In some cases, a capacitivecoupling is used to look for broad band noise that often accompany arcs.In particular, all such devices look for unusual behavior in eithervoltage changes or changes of frequency spectrum, and consider thesechanges as indicators of the presence of arcing. The arc detectioncircuit then communicates via link 406 to the system management unit104, signaling that the detector 404 has detected an arc. Systemmanagement unit 104, in response to the signal from detector 404, theninitiates a test, which is described below in the discussion of FIG. 5.For the purposes of the system and method described herein, noparticular type should be considered better than any other type, as longas it has the capability to detect arcing in a dc circuit, as it is usedherein.

FIG. 5 shows a representative testing process 500 for detecting arcswithin a solar energy system, according to one aspect of the system andmethod disclosed herein. At point 501, the system receives a signalindicating detection of an arc and initiates the test. At step 502, thesystem evaluates the signal value; for example, depending on the arcdetection circuitry employed, different types of arcs and differentstrengths or danger levels may be indicated, rather than simply thepossible presence of an arc. In step 503, the system assembles a list ofpotentially affected panels, including the LMU numbers.

As described above, in the discussion of FIG. 3, if arc detectors areattached individually to each of strings 310 a-n, then only panels inthe indicated string require testing. However, if the arc detectiondevice is attached to combiner box 106, then all panels in all thestrings connected to the combiner box 106 must be tested. In step 504,the system increments the unit count i to 1 and, in step 505, turns thepanel off. In step 506, the system holds the unit in an off state for aduration t, and upon the completion of duration t, in step 507, thesystem checks to determine whether the arcing signal has ceased. If thesignal has not ceased, the system moves to step 508, where it turns onpanel i, and then to step 509, where it increments the unit count i toi+1.

In step 510, the system determines whether the current count i isgreater than the number of panels u. If, at step 510, the systemdetermines that i is less than u, the system loops back to step 505 andexecutes the test on the next panel. If, at step 510, the testing hasreached a point where i is equal to or greater than u, the systemconcludes 511 that the problem lies outside the panels, perhaps in thewiring. In step 512, the system compiles a report and sends it to anenergy system service monitoring company, and in step 513, the testends. If, at step 507, the system determines that the arcing signal hasceased after testing a panel, the system notes the panel number, whichit sends to the report compiler in step 512, and then the process loopsback to step 509, where the unit number is incremented and the testingcontinued, in case some other units are also arcing.

Depending on the topology of system 300, in some cases an LMU may haveat least one additional switch (on line 112 opposite Q1, not shown) inthe LMU 102 x shown in FIG. 2 allowing to completely disconnect thesolar module 101 x from the string bus 105 (respectively connections 112and 114) to completely insulate the solar cells from the string. Inother cases, there may be only a single switch, which in some cases maynot permit complete insulation, requiring that the whole string beturned off at the combiner box, for example, for safety reasons. At thesame time, the system can notify the service company, which can thendeliver and install a replacement panel in a very short time, reducingthe energy system down-time dramatically.

In the foregoing specification and the following appended documents, thedisclosure has been described with reference to specific exemplaryembodiments thereof. It will be evident that various modifications maybe made thereto without departing from the broader spirit and scope asset forth in the following claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

While the particular system, apparatus, and method for arc detection andIntervention as herein shown and described in detail, is fully capableof attaining the above-described objects of the inventions, it is to beunderstood that it is the presently preferred embodiment of the presentinventions, and is thus representative of the subject matter which isbroadly contemplated by the present inventions, that the scope of thepresent inventions fully encompasses other embodiments which can becomeobvious to those skilled in the art, and that the scope of the presentinventions is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular means“at least one”. All structural and functional equivalents to theelements of the above-described preferred embodiment that are known orlater come to be known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the present claims. Moreover, it is not necessary for adevice or method to address each and every problem sought to be solvedby the present inventions, for it to be encompassed by the presentclaims. Furthermore, no element, component, or method step in thepresent disclosure is intended to be dedicated to the public, regardlessof whether the element, component, or method step is explicitly recitedin the claims.

What is claimed is:
 1. A photovoltaic system, comprising: a plurality ofphotovoltaic panels; a plurality of local management units coupled tothe plurality of photovoltaic panels respectively, each respective localmanagement unit of the plurality of local management units coupled to arespective photovoltaic panel of the plurality of photovoltaic panels toreceive electricity generated by the respective photovoltaic panel andconvert the electricity into an output; a set of wires connectingoutputs of the local management units; an arc detector coupled to theset of wires to detect arc occurrences; and a system management unit incommunication with the arc detector and the local management units;wherein the system management unit is configured to identify a locationof an arc by at least communicating to a first local management unit inthe plurality of photovoltaic panels to turn off an output of the firstlocal management unit and determining absence of arc detected by the arcdetector in a predetermined period of time after turning off the outputof the first local management unit.
 2. The system of claim 1, whereinthe arc detector is configured to detect an arc occurrence in the systemvia detecting a signal in the set of wires.
 3. The system of claim 2,wherein the signal corresponds to a voltage change.
 4. The system ofclaim 2, wherein the signal corresponds to a frequency spectrum change.5. The system of claim 2, wherein in response to a communication fromthe arc detector indicating a detected arc occurrence in the system, thesystem management unit is configured to identify a subset of theplurality of local management units.
 6. The system of claim 5, whereinthe system management unit is configured to instruct local managementunits in the subset to turn off outputs for at least the predeterminedperiod of time to determine whether the arc detector detects arcoccurrences during a time period in which outputs of local managementunits in the subset are turned off.
 7. The system of claim 5, whereinthe system management unit is configured to instruct local managementunits in the subset to turn off outputs sequentially, wherein each oflocal management units in the subset is instructed to turn off outputsfor the predetermined period of time.
 8. An apparatus, comprising: asystem management unit for a photovoltaic system, the system having aplurality of photovoltaic panels; a plurality of local management unitscoupled to the plurality of photovoltaic panels respectively, eachrespective local management unit of the plurality of local managementunits coupled to a respective photovoltaic panel of the plurality ofphotovoltaic panels to receive electricity generated by the respectivephotovoltaic panel and convert the electricity into an output; a set ofwires connecting outputs of the local management units; and an arcdetector coupled to the set of wires to detect arc occurrences; andwherein the system management unit is configured for communications withthe arc detector and the local management units in the photovoltaicsystem; and wherein the system management unit is configured to identifya location of an arc by at least communicating to a first localmanagement unit in the plurality of photovoltaic panels to turn off anoutput of the first local management unit and determining absence of arcdetected by the arc detector in a predetermined period of time afterturning off the output of the first local management unit.
 9. Theapparatus of claim 8, wherein the arc detector is configured to detectan arc occurrence in the system via detecting a signal in the set ofwires.
 10. The apparatus of claim 9, wherein the signal corresponds to avoltage change.
 11. The apparatus of claim 9, wherein the signalcorresponds to a frequency spectrum change.
 12. The apparatus of claim9, wherein in response to a communication from the arc detectorindicating a detected arc occurrence in the system, the systemmanagement unit is configured to identify a subset of the plurality oflocal management units.
 13. The apparatus of claim 12, wherein thesystem management unit is configured to instruct local management unitsin the subset to turn off outputs for at least the predetermined periodof time to determine whether the arc detector detects arc occurrencesduring a time period in which outputs of local management units in thesubset are turned off.
 14. The apparatus of claim 12, wherein the systemmanagement unit is configured to instruct local management units in thesubset to turn off outputs sequentially, wherein each of localmanagement units in the subset is instructed to turn off outputs for thepredetermined period of time.
 15. A method in a photovoltaic system, themethod comprising: providing a plurality of photovoltaic panels and aplurality of local management units coupled to the plurality ofphotovoltaic panels respectively, each respective local management unitof the plurality of local management units coupled to a respectivephotovoltaic panel of the plurality of photovoltaic panels to receiveelectricity generated by the respective photovoltaic panel and convertthe electricity into an output, wherein a set of wires connect outputsof the local management units; and receiving, in a system managementunit of the photovoltaic system, a communication from an arc detectorcoupled to the set of wires, the communication indicating an arcoccurrence detected by the arc detector; and identifying, by the systemmanagement unit, a location of an arc by at least: communicating to afirst local management unit in the plurality of photovoltaic panels toturn off an output of the first local management unit, and determiningabsence of arc detected by the arc detector in a predetermined period oftime after turning off the output of the first local management unit.16. The method of claim 15, wherein the arc detector is configured todetect an arc occurrence in the system via detecting a signal in the setof wires.
 17. The method of claim 16, wherein the signal corresponds toone of: a voltage change, and a frequency spectrum change.
 18. Themethod of claim 16, further comprising: in response to the communicationfrom the arc detector, identifying, by the system management unit, asubset of the plurality of local management units.
 19. The method ofclaim 18, further comprising: communicating, by the system managementunit, with local management units in the subset to turn off outputs forat least the predetermined period of time to determine whether the arcdetector detects arc occurrences during a time period in which outputsof local management units in the subset are turned off.
 20. The methodof claim 18, wherein the system management unit is configured toinstruct local management units in the subset to turn off outputssequentially, wherein each of local management units in the subset isinstructed to turn off outputs for the predetermined period of time.